Commercially prepared zonally and chromatographically purified bivalent (A/England-B/Mass) and monovalent (B/Hong Kong) inactivated influenza vaccines were given to 438 individuals 6-33 years old. The vaccines had been examined for antigen content by chick cell agglutination (CCA) tests and electron microscopic particle count determinations. Endotoxin and pyrogen content were determined by limulus amebocyte lysate (LAL) and rabbit pyrogenicity assays; and egg-associated protein contamination was estimated by total protein and single radial immunodiffusion assays. Although great differences (10-200-fold) were found in the amount of endotoxin or pyrogen in the vaccines, no significant differences were found in the febrile responses they induced. Both bivalent and monovalent vaccines induced fever of greater than or equal to 38 C at a rate of approximately 3 1/2-4% above background. The febrile responses were most frequent at 24 hours after inoculation and a higher rate was observed in children than adults. Local reactions consisting of tenderness, erythema or induration were seen in from 20-57% of the recipients and also were unrelated to the pyrogenic or host-derived materials in the vaccines. Adults had higher local reaction rates than children and some vaccines containing larger amounts of viral antigen induced significantly higher rates of reactivity than did vaccines containing smaller amounts of antigen. Although 37-51% of all recipients experienced either a local and/or febrile reaction to influenza immunization, the reactions were in general mild and would not consitute a significant disadvantage in the immunization of children over 6 years and adults to prevent influenza infection and its sequelae.